{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Error Trapping for Database Errors"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import psycopg2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Connecting with invalid credentials"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "USER = 'postgres'\n",
    "PASSWORD = 'someinvalidpassword'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "ename": "OperationalError",
     "evalue": "FATAL:  password authentication failed for user \"postgres\"\n",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mOperationalError\u001b[0m                          Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-5-cc7c715f4132>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n\u001b[0m\u001b[0;32m      2\u001b[0m                                         \u001b[0muser\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mUSER\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      3\u001b[0m                                         \u001b[0mpassword\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mPASSWORD\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      4\u001b[0m                                         host='localhost')\n",
      "\u001b[1;32mC:\\ProgramData\\Anaconda3\\lib\\site-packages\\psycopg2\\__init__.py\u001b[0m in \u001b[0;36mconnect\u001b[1;34m(dsn, connection_factory, cursor_factory, **kwargs)\u001b[0m\n\u001b[0;32m    125\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    126\u001b[0m     \u001b[0mdsn\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0m_ext\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mmake_dsn\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mdsn\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;33m**\u001b[0m\u001b[0mkwargs\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m--> 127\u001b[1;33m     \u001b[0mconn\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0m_connect\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mdsn\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mconnection_factory\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mconnection_factory\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;33m**\u001b[0m\u001b[0mkwasync\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m    128\u001b[0m     \u001b[1;32mif\u001b[0m \u001b[0mcursor_factory\u001b[0m \u001b[1;32mis\u001b[0m \u001b[1;32mnot\u001b[0m \u001b[1;32mNone\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    129\u001b[0m         \u001b[0mconn\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mcursor_factory\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mcursor_factory\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mOperationalError\u001b[0m: FATAL:  password authentication failed for user \"postgres\"\n"
     ]
    }
   ],
   "source": [
    "conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n",
    "                                        user=USER,\n",
    "                                        password=PASSWORD,\n",
    "                                        host='localhost')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Exception Handling"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "FATAL:  password authentication failed for user \"postgres\"\n",
      "\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n",
    "                                        user=USER,\n",
    "                                        password=PASSWORD,\n",
    "                                        host='localhost')\n",
    "except psycopg2.OperationalError as err:\n",
    "    print(err)\n",
    "    conn = None"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "None\n"
     ]
    }
   ],
   "source": [
    "print(conn)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "----------"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "-----------"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Challenge"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Your python web application is failing with an unhandled excpetion because an attempted connection to the database failed.\n",
    "\n",
    "- What Python programming statement would you use to trap the error?\n",
    "\n",
    "- What Algorithm would you use in the error handling code to attempt reconnects to the database?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Solution"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- try except clause\n",
    "- exceptional back off approach"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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